1. Field of the Invention
The invention relates to a rolling-ball switch, more particularly to a rolling-ball switch that is easy to assemble and to a method of making the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional rolling-ball switch 10, as disclosed by the applicant in Taiwanese Patent No. 155965, includes an insulated cover body 11, a conductive ball 12 disposed in the cover body 11, four terminal rods 13, and an insulated bottom seat 14. The insulated cover body 11 is made of plastic, and has a hollow rectangular shape. The cover body 11 has a bottom opening 111, and two opposite inward protrusions 112 projecting from an inner wall of the cover body 11 adjacent to the bottom opening 111. The insulated bottom seat 14 is made of plastic, and has four spaced-apart through holes 141, and two opposite grooves 142 (only one is visible) provided on an outer face of the bottom seat 14 to engage the protrusions 112, respectively. Each of the terminal rods 13 has opposite first and second tapered ends 131, 132. The width of each terminal rod 13 is larger than a diameter of a respective one of the through holes 141.
To assemble the conventional rolling-ball switch 10, the conductive ball 12 is initially disposed inside the cover body 11, and the terminal rods 13 are subsequently inserted into the respective through holes 141. The bottom seat 14 is then inserted into the cover body 11 through the bottom opening 111 so as to confine movement of the conductive ball 12 within a receiving space 15 defined by the cover body 11 and the bottom seat 14. At this time, the protrusions 112 and the grooves 142 are respectively engaged to each other, and the conductive ball 12 is movable toward or away from the first tapered ends 131 of the terminal rods 13. Finally, an epoxy resin 114 is filled within a space 113 defined by a bottom end wall of the cover body 11 and a bottom surface of the bottom seat 14.
The conventional rolling-ball switch 10 may be applied to an electrical appliance, such as an electric heater (not shown), that is ideally maintained in an upright state. When the electrical appliance is in use and in an upright state, the conductive ball 12 is in contact with the first tapered ends 131 of the terminal rods 13 so as to maintain the electrical appliance in an ON state. When the electrical appliance is tipped to one side or completely tipped over due to an external force, the conductive ball 12 rolls away from the first tapered ends 131 of the terminal rods 13 so as to switch the electrical appliance to an OFF state. Hence, safe use of the electrical appliance is enhanced.
Although the aforementioned conventional rolling-ball switch 10 can achieve its intended purpose, it has the following drawbacks:
1. To ensure optimum quality of the conventional rolling-ball switch 10, the conductive ball 12 must contact the first tapered end 131 of each terminal rod 13 at a similar angle, that is, the heights of the first tapered ends 131 of the terminal rods 13 must be equal. Because each terminal rod 13 is configured as a separate, individual body, ensuring that the first tapered ends 131 of the terminal rods 13 have equal heights after insertion into the respective through holes 141 complicates the steps of assembly of the conventional rolling-ball switch 10. As a result, the assembly of the conventional rolling-ball switch 10 is time-consuming.
2. With reference to FIG. 3, even when care is taken during assembly, the first tapered ends 131 of the terminal rods 13 are nevertheless not equal in height and have a height difference (I). If the switch 10 tilts rightwards, the conductive ball 12 will move rightwards and away from the left terminal rod 13. If the switch 10 tilts leftwards, the conductive ball 12 will move leftwards and away from the right terminal rod 13. Because the left and right terminal rods 13 are different in height, however, the tilting angle of the switch 10 that causes the conductive ball 12 to move away from the left terminal rod 13 will be different from the tilting angle that causes the conductive ball 12 to move away from the right terminal rod 13. Therefore, the movement of the conductive ball 12 is not uniform when the switch 10 is subjected to external forces so that the ON/OFF operations of the switch 10 become less stable and imprecise.